Antonio Conte's side won 3-2 at Atalanta, who hadn't lost since September, and moved six points clear of second-placed Inter Milan.
Inter have two matches in hand and host lowly Empoli on Sunday (Monday AEDT).
Atalanta remained third but fell seven points behind Napoli.
Atalanta knew they could gain a major boost to their own title hopes with a win on Saturday (Sunday AEDT). They were unbeaten in their past 15 league matches, but had faltered of late, drawing their past three games.
However, they took the lead in the 16th minute with a ferocious finish into the top left corner from league-leading goal-scorer Mateo Retegui, back in the starting line-up after injury.
But Matteo Politano levelled in similar fashion in the 27th  minute, and Scott McTominay turned the match around completely for Napoli five minutes from halftime.
Ademola Lookman equalised 10 minutes after the break with a fine solo goal, skipping past one challenge and holding off several Napoli players before firing into the far bottom corner.
Then Romelu Lukaku headed in what proved to be the decider 12 minutes from time.
In other action, Tim Weah scored against his father's former club as Juventus beat AC Milan 2-0 to inflict Sergio Conceicao's first loss as the Rossoneri coach.
Weah, whose father is former world player of the year George Weah, was substituted on for the injured Kenan Yildiz at halftime, and fired Juventus 2-0 up in the 64th minute.
Samuel Mbangula had scored the opener five minutes earlier.
Conceicao's reign started with three wins and a draw in four matches, including a win over Juventus in the Italian Super Cup semi-finals this month.
Juventus moved up to fourth, six points above eighth-placed Milan.
Bologna were up to sixth after scoring a 3-1 win over bottom club Monza.
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